1. Field of the Invention
The present invention relates to a conveyor roller drive device for driving the conveyor rollers of a conveyor system by rotational power provided by a power generator. The present invention also relates to a drive roller assembly with the conveyor roller drive device combined with the conveyor rollers.
2. Description of the Related Art
Conventionally, conveyor systems for conveying various goods have been widely used in every aspect of whatever the industrial field.
In general, such a conveyor system includes a plurality of conveyor rollers, and one or more of the conveyor rollers are rotated by means of the conveyor roller drive device. It is to be understood that the combination of the driven conveyor rollers and the conveyor roller drive device is herein referred to as the drive roller assembly.
Incidentally, the concept of the conveyor system includes two types of conveyor systems, one type of system for allowing the conveyor rollers to directly contact with and convey goods, and the other type of system, having a conveyor belt wound around a plurality of conveyor rollers, for allowing the conveyor belt to convey the goods.
In recent years, such a drive roller assembly of motor roller type has been realized which houses a conveyor roller drive device inside the conveyor rollers. Such a configuration allows motor or the like to disappear when viewed from outside. Thus, this makes it possible to provide a more functional design to the system and thereby allows the production line of a factory to look tidy in addition to a reduction in size and weight of the conveyor system.
FIG. 8 illustrates a drive roller assembly 10 of this type. The drive roller assembly 10 functions as a motor roller, in which a conveyor roller drive device 16 (hereinafter referred to as the drive device) is housed inside a cylindrical barrel portion 14 of a conveyor roller 12.
The drive device 16 includes a motor 18 or a type of power generator, a gear reducer 20 provided in the motor 18, and a coupling portion 22, coupled to the barrel portion 14, for transmitting output from the gear reducer 20 to the conveyor roller 12. At the rear side of a casing 24 of the motor 18, a support shaft 24a is provided integrally therewith and fixed to an external member 26 (the overall configuration thereof is not shown; for example, which corresponds to a conveyor frame). Two bearings 28 are provided inside the casing 24 and rotatably support a motor shaft 30.
The gear reducer 20 is a three-stage reduction configuration having first to third simple planetary gear mechanisms 32, 34, 36, in which each of the simple planetary gear mechanisms 32, 34, 36 has a sun gear T, a planetary gear Y, a ring gear R, and a carrier C. In this configuration, all the ring gears R are integrally formed in a gear box 38, a rotational power is input to the sun gear T, and the rotational power is output from the carrier C. The gear box 38 is fixed to the casing 24 of the motor 18.
The sun gear T of the first simple planetary gear mechanism 32 is formed directly on the end portion of the motor shaft 30 and thereby allows the power of the motor 18 to be input. In addition, the carrier C of the third simple planetary gear mechanism 36 is provided with an output shaft 40 of the gear reducer 20. The coupling portion 22 has a cylindrical projection 22b formed at the center of a disc-shaped plate portion 22a. The output shaft 40 is fixedly inserted in the projection 22b, and the periphery of the plate portion 22a is fixed with screws 22c to the barrel portion 14. This configuration allows the power of the motor 18 to be reduced by means of the gear reducer 20 and in turn transmitted to the conveyor roller 12 via the coupling portion 22.
On the outer periphery surface of the projection 22b of the coupling portion 22, there is provided a bearing 41, which holds the output side of the gear box 38.
The barrel portion 14 of the conveyor roller 12 is covered at both the axial ends thereof with circular side discs 42 and 44.
The side disc 42 on one end has a through hole 42a formed at the center thereof, where a bearing 46 is provided and the support shaft 24a of the motor 18 penetrates the through-hole 42a and the bearing 46. Accordingly, the side disc 42 (at one end of the conveyor roller 12) is rotatably supported by means of the support shaft 24a. 
Likewise, the side disc 44 on the other end has also a through-hole 44a formed therein, where a bearing 48 is provided. In addition, an independent support shaft 50 or a member separated from the drive device 16 inside the conveyor roller 12 penetrates the through-hole 44a, with the independent support shaft 50 being fixed to the external member 26. Accordingly, the side disc 44 on the other end (of the conveyor roller 12) is rotatably supported by means of the independent support shaft 50.
Inside the support shaft 24a of the motor 18, there is formed a wire guide path through which wiring 52 passes to supply electricity to the motor 18. Since the motor 18 itself is fixed to the external member 26 by means of the support shaft 24a, the reactive force generated upon driving the conveyor roller 12 is received by means of the support shaft 24a. 
As described above, it is possible to directly convey goods or drive the conveyor belt by the rotation of the drive roller assembly 10 that serves as a motor roller.
The drive roller assembly 10 and a part thereof or the drive device 16 can positively transmit power by the engagement of gears. Thus, the drive roller assembly 10 and the drive device 16 are provide with a high torque transmission capability, being suitable in particular for conveying heavy goods.
However, recent years have seen various goods as goods to be conveyed, and accordingly the environment in which the goods are to be conveyed and the function with which the conveyor system has to be equipped have varied. Correspondingly, recent years have found such situations which the aforementioned drive roller assembly 10 or the like cannot sufficiently deal with.
It is not always true that conveyed goods are placed on the conveyor system under a stable condition (in the state of a low center of gravity). For example, goods having a high center of gravity such as long bottles or the like are placed upright in some cases. In these cases, when (the absolute value of) an acceleration in the conveyor system was too high, the conveyed goods readily fell down and thereby the conveyor line had to be temporarily stopped. In addition to this, there was a problem that when the line was temporarily stopped with the conveyed goods remaining placed on the conveyor system, the line had to be restarted from a standstill state to a high speed state of operation, thereby causing the conveyed goods to fall down again.
In order to avoid these problems, it is necessary to employ an inverter (a frequency controller) in addition to the drive device 16 so that the line continues to operate at a low speed with a low acceleration during a start-up and then increases gradually in speed to finally come to a constant high speed. However, the inverter is very expensive (approximately the same cost as the drive roller assembly 10), leading to a substantial increase in cost of the whole system.
In general, these are caused by a torque greater at the start-up than during steady operation. For example, the high-efficiency motor or the like, which has become predominant lately in various fields of application, has the start-up torque approximately four times as great as the rated torque. Accordingly, the line would be subjected to a high start-up torque with or without the inverter, often causing the conveyed goods to fall down.
Furthermore, the rotational load of the conveyor would be significantly varied all of a sudden upon placing heavy goods suddenly onto the conveyor system during operation or upon unloading heavy goods from the conveyor at a time. This variation in load, transmitted directly to the drive roller assembly 10, would present a problem that the support shaft 24a for receiving the reactive torque was subject to damage. Furthermore, the variation in load, directly transmitted to the external member 26 (frame) via the support shaft 24a, would cause vibrations or noise to occur from the frame. To avoid the vibrations and noise, the frame had to be increased in rigidity.
As described above, attempts to satisfy the recent market requirements by means of the drive roller assembly 10 would cause increases in cost in all aspects.
Incidentally, it is preferable that an axial length W of the conveyor roller 12 should be made as short as possible to reduce the weight thereof in order to convey thin members. However, as is obvious from FIG. 8, the axial length W could not be made as short as desired due to the restraint of the size of the drive device 16 which is housed inside the conveyor roller.
This is mainly caused by the configuration of support at both ends in which the gear box 38 is extended in the axial direction to provide the bearing 41 therein and support the motor 18 and the gear reducer 20 on the side of the coupling portion 22. This is because it is difficult in terms of strength to support the motor 18 and the gear reducer 20 only by the support shaft 24a in a cantilever fashion. This can be found obvious from the assumption of the absence of the bearing 41. That is, the motor 18 deflects in a cantilever state, thereby making it extremely difficult to maintain the concentricity of the motor shaft 30 and the output shaft 40 (the carrier C).
The present invention was developed in view of the aforementioned problems. It is therefore the object of the present invention to provide a drive device which can mechanically prevent a sudden acceleration or deceleration and a drive roller assembly which can provide a compact axial length to the conveyor rollers.
To achieve the aforementioned object, the present invention provides a conveyor roller drive device including a power generator for generating rotational power, and a coupling portion, coupled to a conveyor roller of a conveyor system, for transmitting the rotational power of the power generator to the conveyor roller. The conveyor roller drive device is adapted that a traction roller transmission mechanism is disposed in a rotational power transmission path between the power generator and the coupling portion. Here, the traction roller transmission mechanism includes a sun roller, planetary rollers disposed on a periphery of the sun roller to roll in contact with the sun roller, and a ring roller for allowing the planetary rollers to roll in contact with an inner periphery surface of the ring roller.
The inventor considered that the problem such as of the conveyed goods falling down on the conveyor system was hidden in the xe2x80x9cpositive torque transmission by gear engagementxe2x80x9d which would generally be considered to be a merit of the gear. In this structure, the power generator will transmit torque (particularly, a start-up torque and a braking torque) directly to the conveyor rollers, thereby causing conveyed goods to readily fall down upon start-up and breaking. That is, torque is transmitted directly too much, thereby resulting conversely in a demerit.
In this context, according to the present invention, attention has been focused on disposing the traction roller transmission mechanism in the power transmission path of the conveyor roller drive device (hereinafter referred to as a drive device). Unlike the gear engagement, the traction roller transmission mechanism allows power to be transmitted by the traction produced between the rollers, thereby always producing sliding between the input and output elements. In other words, xe2x80x9cslidingxe2x80x9d serves to transmit power.
FIG. 7 illustrates schematically the relationship between the transmission torque of the traction roller transmission mechanism and the sliding (indicated by solid line A). Application of zero torque to the traction roller transmission mechanism causes no sliding to occur, while the sliding increases continuously (in a curve) as the torque increases and a given limit to transmittable torque (which is referred to as the maximum transmission torque) is then reached. Suppose a high torque is input from either side. In this case, as is obvious from this relationship, the sliding produced by the traction roller causes a difference in rotational speed between the input and output, thereby functioning as a xe2x80x9ccushionxe2x80x9d. Suppose that this happens to the gear transmission structure. In this case, as shown by dotted line B of FIG. 7, with the sliding remaining zero all the time, the input torque is directly transmitted to the output side to give a shock to a counterpart machine. (Here, the xe2x80x9cslidingxe2x80x9d is meant not to occur on the tooth face but designates a delay in rotational speed between the input and output.)
For example, suppose the conveyor rollers are driven. In this case, when the torque produced by starting up the power generator is transmitted to the conveyor rollers, the traction roller transmission mechanism which is disposed in the power transmission path allows the sliding to function as a xe2x80x9ccushionxe2x80x9d for the transmission of torque. Accordingly, a sudden rise in drive torque is prevented, thereby making it possible to prevent the conveyed goods from falling down. This happens not only at the time of start-up but also at the time of a sudden acceleration and deceleration.
The present invention is discussed in more detail below. The difference between the start-up torque of the power generator and the load torque of the conveyor roller (which equals the start-up torque minus the load torque) is used as an acceleration torque for accelerating the rotation of the conveyor rollers. With the acceleration torque being too high (i.e., the start-up torque being too high), the rotation of the conveyor rollers is suddenly accelerated, thereby causing the conveyed goods to fall down. However, the present invention allows the traction roller transmission mechanism to slide to act as a xe2x80x9ccushionxe2x80x9d. The conveyor side is not always provided with a predetermined speed (output speed of power generator/acceleration or deceleration ratio). The sliding causes the speed of the conveyor to increase slightly behind an increase in that of the power generator. Thereafter, the amount of sliding of the traction roller transmission mechanism is reduced gradually, finally allowing the conveyor rollers to be shifted to steady operation.
As described above, the cushioning start-up function of the traction roller transmission mechanism creates a difference in time between the power generator side and the conveyor roller side upon transition to the steady state, thereby making it possible to prevent the conveyed goods from falling down.
Conversely, for example, suppose that some external impact is applied to the conveyor system side to result in a variation in load of the conveyor rollers. In this case, the load torque is prevented from being directly transmitted to the power generator side. This is also because the traction roller transmission mechanism functions as a cushion for the transmission of torque. Suppose that a sudden increase in load torque is directly transmitted to the power generator. In this case, as the speed decreases, an increase in torque of the power generator side occurs for a sudden acceleration. Consequently, continuous sudden accelerations and decelerations would cause the conveyed goods to readily fall down. However, the present invention provides the traction roller transmission mechanism. A sudden increase in load torque would thereby allow the sliding to increase and act as a cushion. This allows a drop in speed on the conveyor side to affect not directly but indirectly the power generator side including the (increased) amount of sliding. Accordingly, a sudden variation in torque can be prevented, thereby enabling a comparatively smooth shift (or restoration) to the steady state.
Furthermore, as is obvious from the foregoing results, variations in torque acting upon between the power generator and the conveyor rollers are alleviated. This in turn reduces the vibration to be transmitted to the external frame to which the power generator is fixed Consequently, the burden of the coupling portion between the power generator and the external frame is alleviated. In addition, the rigidity of the external frame needs not to be increased unnecessarily (to prevent vibrations), thereby making it possible to reduce fabrication cost.
Incidentally, an accelerator and decelerator other than the traction roller transmission mechanism can also be incorporated in the power transmission path of the present invention. In other words, it is possible to provide the aforementioned action by disposing at least one traction roller transmission mechanism anywhere in the path.
Furthermore, in the aforementioned invention, it is preferable that a sliding ratio of the traction roller transmission mechanism is set to 0.1% or more and 1.0% or less when a rated torque of the power generator is transmitted to the conveyor roller. With the aforementioned setting, it is possible to allow an offset (a delay) in speed of the conveyor roller side to fall within the aforementioned range during the steady operation of the power generator. Incidentally, the sliding ratio is the difference (the amount of sliding) between the ideal speed (input speed/acceleration or deceleration ratio) and the actual speed of the output element of the traction roller transmission mechanism, the difference being expressed as a percentage to the ideal speed.
It has been already described that the traction roller transmission mechanism has a cushioning function; however, this requires a consideration about the balance between the function and the drive capacity of the conveyor system. Accordingly, in the aforementioned invention, it is preferable that limit transmission torque P of the traction roller transmission mechanism is set so as to satisfy that P greater than 1.0xc3x97T, with respect to an output element converted value T of the traction roller transmission mechanism corresponding to a load torque provided during the steady operation of the conveyor system. The limit transmission torque is obtained by converting the limit torque transmissible by the traction roller transmission mechanism in terms of the output element. For example, suppose the rotational power is input to the input element and a gradually increasing braking torque is provided such as by braking to the output element side in order to measure the limit transmission torque. In this case, the limit transmission torque means the maximum value of the braking torque obtained during the transition in which the sliding gradually increases up to infinity (where no rotation is available to the output element). As described above, the limit transmission torque exceeds the load torque of the conveyor system in steady operation, thereby making it possible to positively drive the conveyor rollers (only in steady operation).
In the foregoing, the conveyor roller drive device for driving the conveyor roller has been described. When integrated with each other, the conveyor roller drive device and the conveyor roller can be considered to be a xe2x80x9cdrive roller assemblyxe2x80x9d. In this case, it is preferable that a motor is employed as the power generator, and the motor, the traction roller transmission mechanism, and the coupling portion are housed inside the barrel portion of the conveyor roller, so that the conveyor roller functions as a motor roller.
In this case, it is desirable that the output element of the traction roller transmission mechanism is fixed to the coupling portion, and the fixed element of the traction roller transmission mechanism is fixed to the casing of the motor, thereby allowing the traction roller transmission mechanism to support the output side of the motor.
In the drive roller assembly of this type, the rear side of the motor is fixed to the external member with the support shaft. However, in the prior art, a separate specially-provided shaft was adapted to rotatably support the front side by a coupling portion or the like. This separate shaft made the structure of the drive device complicated and the conveyor roller longer in the axial direction.
This structure allows the output element of the traction roller transmission mechanism to be fixed to the coupling portion (which also means that the output element is integrated with the coupling portion.). That is, the traction roller transmission mechanism is adapted to allow each roller to roll in contact therewith and can function as a bearing, thereby providing a bearing to the coupling portion in this state. Accordingly, with the fixed element of the traction roller transmission mechanism being fixed to the casing of the motor (irrespective of whether directly or indirectly), the front side of the motor is meant to be supported by the bearing (the traction roller transmission mechanism).
Consequently, the need for a separate special-purpose bearing is obviated and thereby the drive device is simplified, leading to a reduction in weight of the device. Furthermore, the conveyor roller can be made shorter in the axial direction, thereby making it possible to flexibly vary the length in a wider range as required.